The present application generally relates to an engine control arrangement for a watercraft, and more particularly relates to an engine management system that prevents engine damage due to excessive engine speeds.
Watercraft, including personal watercraft and jet boats, are often powered by an internal combustion engine having an output shaft arranged to drive a water propulsion device. Occasionally, watercraft may leave the water at speed due to waves, thus causing sudden decreased load on the propulsion unit, which can raise the engine RPM to a damaging speed.
Watercraft often operate within three modes of operation: displacement mode, transition mode and planing mode. During lower speeds, the hull displaces water to remain buoyant; this is the displacement mode. At a particular watercraft speed relative to the water, a portion of the hull rises up from the water and the watercraft begins planing across the water; this is the planing mode. The transition mode occurs between the displacement mode and the planing mode and involves the range of watercraft speeds between the planing and displacement modes.
While the watercraft is planing (i.e., up on plane), the wetted surface area of the watercraft is decreased and the water resistance is substantially reduced, increasing the likelihood that the propulsion unit will leave the water. On the other hand, once the watercraft slows to a speed that brings the watercraft off plane (i.e., transition mode and/or displacement mode), the wetted surface area of the watercraft is significantly increased and the likelihood of air entering the propulsion unit is dramatically decreased.
One way of protecting the engine against over-revving is to limit the spark plugs from firing, allowing the engine to slow down. In two cycle engines since the spark plugs are fired every stroke, if one firing cycle of a spark plug is stopped in order to slow down the engine, engine smoothness is not significantly compromised. However, in a four cycle engine the spark plugs are fired every second stroke, so when the firing of a spark plug is omitted a noticeable compromise in engine smoothness occurs. Additionally, in any exhaust system where an exhaust catalyst is used, the exhaust catalyst may be damaged due to unburned fuel entering the exhaust system since the fuel injectors continue to operate when the ignition spark is interrupted.
Accordingly, an engine control arrangement has been developed to better control engine speed during a decreased load on the propulsion unit in order to prevent engine damage as well as maintaining a smooth ride. In addition, the engine control arrangement can be configured to maintain a safe engine speed by controlling the fuel injection to varying individual cylinders or to all cylinders gradually.
Thus, one aspect of the present invention is directed to a method of controlling a marine engine associated with a watercraft. The method includes sensing a first engine speed and comparing the first sensed engine speed with a first predetermined speed. Fuel supply to the engine is reduced by a first delivery amount if the first sensed engine speed is above the first predetermined engine speed. The method also includes sensing a second engine speed after reducing fuel delivery by a first fuel amount and restoring fuel delivery by the first fuel amount if the second sensed engine speed is below a second predetermined engine speed that is greater than the first predetermined engine speed.
One aspect of the invention includes the realization that there are operating conditions under which a speed-limiting device can cut engine power when the engine exceeds a first speed, then restore engine power before the engine speed falls below the first speed, without over-revving the engine. This control scenario can allow the engine to operate at an elevated engine speed during a period of reduced load, such as for example but without limitation, when the watercraft jumps slightly out of the water at high speed. By allowing the engine to operate at the elevated speed, the re-entry of the watercraft into the water can be more smooth.
Another aspect of the present invention is directed to a watercraft comprising a hull and an engine disposed within the hull. The engine includes an engine body defining plural cylinders. An engine speed sensor is configured to detect a speed of the engine. The watercraft also includes a controller connected to the engine speed sensor and configured to control a power output of the engine. The controller is configured to detect a first engine speed and to reduce the power output of the engine if the first engine speed is greater than a first predetermined engine speed. Additionally, the controller is configured to detect a second engine speed, and restore the power output of the engine if the second engine speed is less than a second predetermined engine speed, which is greater than the first predetermined engine speed.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.